Packaging tray



C. LAKE PACKAGING TRAY Nov. 5, 1968 2 Sheets-Sheet 1 Filed Sept. 29,1966 FIG! INVENTOR. CONNIE LAKE Nov. 5, 1968 c. LAKE 3,409,199

PACKAGING TRAY Filed Sept. 29, 1966 2- Sheets-Sheet 2 '0 IIIIIIIIIIIIM\\\\\\\\\\\W '0 INVENTOR. CONNIE LAKE United States Patent 3,409,199PACKAGING TRAY Connie Lake, Pittsford, N.Y., assignor to Mobil OilCorporation, a corporation of New York Filed Sept. 29, 1966, Ser. No.583,029 2 Claims. (Cl. 229-25) ABSTRACT OF THE DISCLOSURE The presentinvention relates to molded containers, and more particularly, itrelates to molded containers which are suitable for packaging food forexample and to a process for manufacturing such trays.

A common and conventional problem in the utilization of containers ofany type resides in the storage of such containers. In order to store orship containers, without utilizing a great deal of space, it isnecessary that they be nested one within the other, which practice isconventional.

In general, prior art packaging tray structures have been characterizedin having a bottom wall and side and end walls of a constant and uniformthickness. Additionally, the angle formed between the side and end wallsof the tray with the tray bottom is such that the upstanding side andend walls function to retain product positioned in the tray after it hasbeen overwrapped with, for example, protective plastic or cellophaneoverwrap material, and prevents product from slipping or sliding outsideof the confines of the tray walls. Such trays, i.e. trays with uniformcross section thickness and having side and end walls disposed at acertain minimum angle with respect to the tray base, when they arestacked or nested together contact each other only at the interface ofthe respective side and end walls, there being an opening or dead spacebetween adjacent tray bottom Walls. This dead space results, in additionto increased stack heights which necessitate increased storage space andshipping costs, in permanent deformation of the tray if pressure iapplied to the top or bottom of such a stack. The deformation is causedby the tray bottoms being forced closer together causing a bending orbowing outwardly of the upstanding tray walls.

The support tray structures of the present invention have overcome theaforenoted deficiencies of the prior art trays by providing advantageshitherto unavailable in such trays. The new support trays of the presentinvention may be fabricated from materials, such as plastics or foamedplastics, which materials, since they are compressible, allow trayfabrication from an integral piece of stock material utilizing aone-step molding technique wherein the individual thicknesses of thetray bottom and side and end walls of a tray may be varied. Furthermore,the unique construction of the present support trays re sults in a traywhich may be stacked or nested during storage to give stack heightslower than that achievable with prior art tray constructions resultingin obvious advantages with respect to, for example, shipping costs andwarehouse space savings.

The tray structures of the present invention comprise molded trays ofthermoplastic material comprising a bottom wall, upstanding side and endwalls integral with said bottom wall, the side and end walls of the trayterminating in arcuate corners. The trays are further characiceterizedin that the bottom wall of the tray is thicker than the side and endwalls of the tray.

A better understanding of the invention may be had from the followingdescription read in conjunction with the accompanying drawings wherein:

FIGURE 1 illustrates a top plan view of one form of the support tray ofthe present invention;

FIGURE 2 is a vertical section taken substantially 0n the plane of line22 of FIGURE 1;

FIGURE 3 is a vertical section taken substantially on the plane of line33 of FIGURE 1;

FIGURE 4 is a perspective view of a modified embodiment of the novelfood trays of the present invention;

FIGURE 5 is a vertical section taken substantially on the plane of line5--5 of FIGURE 4.

FIGURE 6 is a cross-sectional view in elevation of a stack of typicalprior art trays;

FIGURE 7 is a cross-sectional view in elevation of a stack of the noveltrays of the present invention such as the tray illustrated in FIGURE 1.

As illustrated in the drawings, the support tray of the presentinvention comprises a substantially fiat tray base, generally indicatedas 11. Side and end Walls 12 and 12 extend upwardly and slightlyoutwardly from base 11 nd are integrally joined to the periphery of traybase 11, said side and end walls terminating in arcuate corners 12"which integrally join side and end wall members 12 and 12. Side and endwalls 12 and 12' are inclined outwardly at a slight angle from thevertical to permit nesting of a plurality of trays for stacking purposesas illustrated in FIGURE 7. This angle. indicated as B in FIGURE 7, mayvary from about 15 up to about 60, however, it has been found preferableif t? is from about to about Side and end walls 12 and 12' terminate inan out wardly flared continuous lip 10 which imparts increased rigidityto the tray structure.

As more clearly illustrated in FIGURES 2 and 3, the thicknesses of thetray base 11 and continuous lip 10 are substantially equal, while thethicknesses of side and end wall members 12 and 12', althoughsubstantially uniform with respect to each other, are considerablythinner than the thickness of tray base 11 or continuous lip 10.

As more clearly illustrated in FIGURE 7, which shows a nestedarrangement of trays fabricated in accordance with the presentinvention, as a result of decreasing the thickness of the side and endWall members 12 and 12' the individual tray base members 11 are incomplete interface contact with one another. This eliminates the deadspace or intervals between the respective tray base portions which arepresent in prior art tray nesting arrangements, as illustrated in FIGURE6, thereby offering the aforediscussed advantages or reduced stackheight and attendant savings on shipping costs and warehouse storage.

In addition to the foregoing advantages, the increased thickness of thetray base results in the tray when nested being in base to base contactwith adjacent tray structures. Accordingly, when pressures, which arenormally encountered during the handling, shipping and storage of suchtray structures, are applied to a nested stack of trays, the side andend walls are not deformed or bowed out as in the case of prior arttrays since the bottom to bottom contact of the trays resist suchdeformative pressures. It has been found that in order to achieve theforegoing advantages, the tray base must be at least 1.3 times as thickas the tray side and end wall members. Although the tray base may bemuch thicker than this, it has been found that when the tray base isover four times the thickness of said side and end walls, excessivestack height of the nested trays results which eliminates theaforediscussed advantages. Furthermore, it has been found that theincreased base thickness of the trays of the present invention, i.e.increased thickness with respect to the side walls thereof, results inan increase of the rigidity of the tray structures of the presentinvention as compared to trays having a uniform profile of thickness.

As will be discussed more 'fully hereinafter, the structural strengthand integrity of the tray is not reduced or sacrificed as a result offorming the tray with side and end walls of reduced thickness, moreover,the method employed for achieving this reduced side and end wallthickness in members 12 and 12' results in a tray which exhibits greaterresistance to deformation than that generally exhibited by a tray of.uniform cross section, i.e. with the side and end wall members being ofsubstantially the same thicknessas the tray base 11.

Depending upon the particular end-use application intended for the traystructures of the present invention, the tray base may vary in thicknessfrom about 50 mils up to about 250 mils while the thickness of the sideand end wall members of the tray may also vary from about 15 mils up toabout 150 mils, provided that the tray base thickness is maintainedatabout at least 1.3 :times the thickness of the side and end wallmembers.

FIGURES 4 and 5 illustrate still another embodiment of the novel traystructures of the present invention. In this instance the inner surfaceof tray base 11 isprovided with a plurality of recesses 14, the bottomportion of each recess terminating at a point 9 above the undersurfaceof tray base 11.

As illustrated in FIGURE 4, the recesses may take the form of a square.However, it should be noted the specific shape of recesses 14 shown inthe drawings is merely for purposes of illustration and that recesses 14may be of any geometrical configuration such as rectangular, triangular,circular, or the like. The side walls 16 of recesses 14 aresubstantially vertical withrespect to the inner surface of tray base 11,the upper edges of recesses 14 being defined by the fiat non-recessedportion of the inner tray surface of tray base 11. As shown in FIGURES 4and 5, the undersurface of tray base 11 is substantially smooth andnon-interrupted. As also illustrated in FIGURE 5, the base 11 is of agreater thickness than side and end wall members 12 and 12' as in thecase of the tray embodiment illustrated in FIGURES 1 through 3 describedhereinbefore.

It has been found that recesses 14 in the upper surface 13 of tray base11 function to mechanically entrap and retain therein liquids, forexample meat or poultry juices,which may be exuded from the meat orpoultry products packaged in such trays. At the same time, as

a result of the inherently hydrophobic character of the plastic materialfrom which the tray is fabricated, these juices will not penetrate thetray beyond the confines of recesses 14, thereby avoiding thedehydrative effects of moisture absorbing tray materials as well asmaintaining the structural integrity and strength of the tray structure.It has been found that the size of the cross-sectional area of recesses14 contributes to a great extent to the ability of the recesses to trapand hold liquids. The recesses are preferably about V8" in diameter andmay vary from about to about 7 in diameter and still function to entrapand retain liquids. However, below these limits there is a tendency forthe liquids not to flow into the recess and, conversely, above theselimits although liquids will enter the recess they will not be entrappedtherein and will have a tendency to flow out of the recess when the trayis tilted or inverted during handling. The depth of recesses 14 has beenfound to have little or no effect on the mechanical functioning of therecess and may vary within wide limits depending only upon the traythickness (i.e. the recess must terminate prior to penetratingcompletely through the tray) and the relative amounts of liquid it isdesired to entrap and retain therein.

Among some of the types of plastic materials which are suitable forfabrication into the tray structures of the present invention arepolyolefins such as polyethylene,

polypropylene, and polybutene; polystyrene; high impact polystyrene;polyurethane; polyvinylchloride and others. A particular material whichhas been found to be well suited for fabrication of the present traystructures is foamed polystyrene. The closed-cell structure of thefoamed polystyrene prohibits absorption or penetration of liquids intothe tray body' and the foam material itself is extremely light weightpermitting ease of handling and transport. i

As hereinbefore indicated, a preferred material employed in theformation of the" tray structures of the present invention is plasticand in particular foam thermoplastic materials and especiallypolystyrene foam. The polystyrene foam may be manufactured utilizinganyone of the number of conventional extrusion techniques, for example,extrusion of foamable polystyrene be ads,. i.e. beads which have ablowing agent already incorporated in them prior to delivery to anextrusion apparatus. or, for example, by direct injection extrusiontechniques wherein a foamable agent isadded to a molten mass ofpolystyrene contained within an extruder prior to extrusion thereof froma die orifice. A

'After the polystyrene foam sheet material has been produced utilizingconventional extrusion techniques as discussed above, it may be moldedto form the tray structures of the present invention. In general, it isdesirable to preheat the foamed polystyrene sheet before it is molded inorder to assure that the sheet will be at a sufficiently elevatedtemperature to permit rapid forming of the desired tray structure in themold. h

After preheating the formed polystyrene foam sheet, the support traystructures of the present invention may be conveniently formed utilizinga molding operation such as match molding, for example. 3

The thickness of the tray base portion of the tray structures of thepresent invention may vary within wide limits depending primarily uponthe nature of the tray material, the side and end wall members of thetray being of a reduced thickness relative to the thickness of the' traybase portion. For example, trays fabricated from a relatively dense traymaterial such as high-impact polystyrene which is extremely rigid wouldrequire less thickness than trays fabricated from low densitypolyethylene. Utilizing the preferred tray forming material of thepresent invention, i.e. polystyrene foam, it has been found thatthicknesses of from about mils, for high density polystyrene foam, toabout 400 mils, for low density polystyrene foam, may be employed, thespecific thicknesses depending primarily upon foam density. Whenfoam'material having preferred density of about 4 pounds per cubic footis employed, an average tray base thickness of from about to about 250mils has been found to be satisfactory. i

The process employed for forming the present trays may best beunderstood by a description of a specific embodiment as illustrated inthe following example, however, such a description is solely forpurposes of illustration and is not to be construed in a limiting sense.For example, the following embodiment sets forth rather specific processand operating conditions employed when preformed polystyrene foam isemployed as the starting material for the tray structure and, of course,such'con- 'ditions will normally vary when other plastic tray materialsare employed. l

' Example I v A preformed sheet of polystyrene foam material with anaverage density of about 4 pounds per cubic ft. and approximately milsthick was fed into a radiant preheat oven and heated to a temperature ofapproximately 275 F. Upon emerging from the preheat oven, thepolystyrene sheet was approximately 200 mils thick as a re.- sult of theexpanding action of the residual blowing agent, in this case pentane,which remains entrapped within the polystyrene cells after it isextruded. The residencetime of the polystyrene in the oven wasapproximately 5 to 20 seconds and the average line speed was about 45ft. per minute. Immediately upon emergence from the preheat oven, thepolystyrene foam sheet passes into a tray forming mold. Thethermoforming mold employed is essentially an internally cooled femalemold base member and an upper male tray forming member. As the matchmold is cycled, the upper mold member presses down on the heatedpolystyrene foam forcing it to assume the traylike configuration of thefemale base member. The cleartance between the mold members is such thatthe base of the tray formed is approximately 200 mils thick and the sideand end wall members are approximately 100 mils thick. The side and endwall members of the tray comprise a compressed form of the polystyrenefoam formed as a result of compressive forces acting against these wallmembers while in the thermoforming device. The peripheral lip borderingthe side and end wall members is approximately 200 mils thick.

Example 11 The formed tray fabricated in accordance with Example I afterbeing removed from the thermoforming device was passed through a heateddie punch employed for forming recesses on the inner surface of the traybottom as illustrated in FIGURES 4 and 5 of the attached drawings. Thedie punch is formed from metallic materials and preferably a metallicmaterial which exhibits good thermal conductivity properties. Aluminumhas been found to be an effective material. The face of the die carriesa plurality of integrally connected projecting aluminum lugs arranged onthe face of the die in a predetermined pattern depending upon the thetray recess pattern desired. The lugs may be coated with a material suchas Teflon, for example, to avoid sticking to the polystyrene workmaterial during the recess forming operation. The size and shape of thelugs may vary depending upon the size and shape of recesses desired uponthe tray surface. However, the cross-sectional area of the recessforming lugs must be within the crosssectional ranges discussed above,i.e. between about and 7 which are necessary to insure properfunctioning of the tray recesses. The temperature of the die isregulated according to the die cycling speed which in turn is dependentupon the in-line speed of the forming operation. Hence, when thedie-punch is cycling at 0.3 second, for example, it has been foundadvantageous to employ die temperatures of from about 575 F. to about625 F. On the other hand, if the line speed is comparatively slow andthe die punch is cycling at three second intervals, for example, dietemperatures as low as about 250 F. have been found to be sutficient forforming the recesses on the inner surface of the tray bottom. As therecess-forming die-punch is cycled, the heated lugs on the die face comeinto contact with the inner surface of the alreadyformed tray bottom,each heated lug advancing through the polystyrene to a point just abovethe lower surface of the tray bottom whereupon the die is removed. Theresultant, finished tray now carries a plurality of recesses,corresponding to the shape and patterned arrangement of the lugs on thesurface of the die-punch.

The number, arrangement and spacing of the recesses on the interiorsurface of the tray bottom may vary depending upon the size of the trayand the quantities of liquid it may be necessary to entrap. Generally,for most meat and poultry packaging operations, the recesses will occupya total area ranging from about 5 percent to about percent of the totalsurface area of the tray bottom and preferably about 15 percent to about25 percent of the total surface area of the tray bottoms interiorsurface.

When recesses on the order of A; in width are employed, it has beenfound convenient to space them on A centers on the interior surface ofthe tray bottom.

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to, without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchvariations and modifications are considered to be within the purview andscope of the appended claims.

What is claimed is:

1. A molded rectangular tray of foam polystyrene material comprising afiat bottom wall, upstanding side and end walls integral with saidbottom wall and extending upwardly and slightly outwardly from saidbottom wall, said side and end walls terminating in arcuate corners,said tray being further characterized in that the bottom wall has athickness of from about 1.3 to about 4 times the thickness of said sideand end walls, said side and end walls being further characterized ascomprising a higher density foam polystyrene material than said bottomwall, said tray being further characterized by being nestable so that innested form the upper surface of the bottom portion of one tray is insubstantial contact with the bottom surface of the bottom portion of anadjacent tray.

2. A molded tray in accordance with claim 1 wherein said tray base ischaracterized by having a plurality of liquid entrapping recessesarranged in a predetermined pattern on the surface thereof.

References Cited UNITED STATES PATENTS 2,893,877 7/1959 Nickolls 991743,040,949 6/ 1962 Foote 2292.5 3,220,631 11/1965 Reifers 229-2.53,264,120 8/1966 Westcott 229-2.5. X 3,305,158 2/ 1967 Whiteford 2292.5

OTHER REFERENCES Koppel-s: Bulletin C-9-273, Apr. 15, 1962, page 3.

DAVID M. BOCKENEK, Primary Examiner.

